Applicator devices, also known as application heads, are known for sheet application of liquid material, in particular hot melt adhesive. Such application heads have a main body, a nozzle assembly for dispensing the liquid material, and a valve system for controlling the dispensing of material. The nozzle assembly and the valve system are incorporated into the main body. The hot melt adhesive is fed to the main body under pressure and is directed from there to the valve system. Directing the adhesive from the main body to the valve system is controlled by the valve system, which also controls the dispensing of the hot melt adhesive from the nozzle assembly for application onto an application surface.
The nozzle assembly has at least one slit for this purpose, to ensure film-type or strip-type dispensing of the liquid material. The slit can have interruptions for this purpose, in order to output a plurality of strips side-by-side, possibly even at differing intervals from each other. In some cases the valve system has a plurality of slits that are controllable independently of each other.
The hot melt adhesive is fed to the main body at a high temperature, which may be, for example, up to 200° C. To avoid too great a temperature drop, heating devices are provided in the main body.
The valve system is attached to the main body by means of screw fittings. To achieve a definable orientation of the valve system with respect to the main body, and thus to the application surface during operation, drilled holes with corresponding pins are provided in the main body and the valve system.
A disadvantage here is that changing the nature and arrangement of the application of the hot melt adhesive, i.e., changing the application pattern—known as a format change—necessitates completely loosening all of the screws attaching the valve system to the main body. This makes a format change costly and also difficult, since both the loosened screws and the nozzle orifice can fall off when the last screw is loosened. Added to this is the fact that a detailed constructional adaptation of the valve system to the main body is necessary.
Another disadvantage with known applicator devices is that different material thicknesses of the hot melt adhesive can occur, depending on the position of the applied hot melt adhesive along the nozzle slit. Such a variation of the material thickness can be caused by an uneven temperature distribution.
The object of the present invention is thus to reduce the above-named problems as much as possible, or to eliminate them.